Benzo[C]cinnoline and its derivatives have been used in various fields, for instance, as raw materials for useful fine chemicals. There have been known the following three routes of preparing the benzo[C]cinnolines by using different starting materials, respectively.
The first route contains methods of reducing 2,2'-dinitrobiphenyls, in which the reduction is conducted by electrolytic reduction in diluted ethanol or by using a reducing agent such as triethyl phosphite, triphenyl phosphine, sodium amalgam or the like. According to these reduction methods, by-products are produced in large quantities and the yields of the benzo[C]cinnolines are at most about 10 - 50%.
The second route is of using 2,2'-diaminobiphenyls as starting materials, which are converted to the corresponding diazonium salts and then subjected to Sandmeyer reaction using bromides or the like. According to these methods, the yields of the benzo[C]cinnolines are at most about 50% and carbazoles are produced as by-products.
The third route is of using azobenzenes as starting materials, which are reacted with aluminum chloride in the presence of sodium chloride or irradiated with light in concentrated sulfuric acid or aqueous solution containing ferric chloride. According to these methods, the yields of the benzo[C]cinnolines are at most about 45%.
Above mentioned conventional methods have such disadvantages that the yields of the objective compounds are about 50% or less, by-products are produced in large quantities and many steps are required in order to separate and purify the objective compounds.
An object of the present invention is to solve such conventional disadvantages.
An other object of the present invention is to provide a method for preparing benzo[C]cinnoline and its derivatives with high yields.
A further object of the present invention is to provide a method for preparing benzo[C]cinnoline and its derivatives with high yields by using 2,2'-diazidobiphenyl and its derivatives as starting materials and utilizing photo-reaction.
The foresaid objects and other objects and advantages of the present invention will become more apparent from the following description.